40 PRACTICAL PARASITOLOGY 



from one another considerably in structure, however. Quite distinct 

 from these, again, is Costia, a parasite met with among fish. 



(a) Trichomonas and Trichomastix. 



The Trichomonas are characterized by their small size, their pear- 

 like shape, and by the possession of four flagella which, with the 

 cytostome, are placed close together at one end. Of these, three of 

 about equal length are true flagella, which frequently adhere to one 

 another at the base, while the fourth forms an undulating membrane. 



To this group belong two parasites of man, T. intestinalis and 

 T. vaginalis. T. intestinalis is a parasite of the small intestine, frequently 

 met with but apparently harmless. It is occasionally found in the 

 stools in diarrhoea, and its presence in the stomach in gastric affections 

 (especially carcinoma) has been proved by means of the stomach-pump, 

 T. vaginalis is frequently found in the vaginal mucus of women. It 

 may also be transferred to the urethra and pass thence into the bladder, 

 where it may give rise to cystitis. Secretion containing parasites 

 should be examined as soon as possible after it is voided. Owing to 

 their extreme activity, the Flagellates are easily seen, and especially so 

 in centrifugalized urine. But if the secretion is allowed to stand for 

 some time, and more particularly if it is kept at room temperature, 

 active movement ceases. Like the intestinal Infusoria, however, the 

 activity of T. vaginalis may be prolonged by keeping the secretions at 

 body temperature. 



Varieties of Trichomonas closely resembling those of man, and of 

 which very little is at present known, are found in the intestines of 

 different mammals, as also in the guinea-pig, mouse, and rat. These 

 are very useful for demonstration purposes. A similar variety, T. 

 lacertcz, Prow, (nee Dofl.), is found in the rectum of Lacertians ; it is, how- 

 ever, somewhat rare. Another form closely resembling it, Trichomastix 

 lacertce, Blochm., is more frequently met with in the rectum of lizards 

 (both Lacerta agilis and L. muris), and this will well repay examination. 

 It differs from Trichomonas in having no undulating membrane, the 

 flagellum, which is turned backwards, forming a free trailer. More- 

 over, the three principal flagella proceed from a basal structure placed 

 upon one side of the organism, while the trailing flagellum proceeds 

 from another similar structure upon the other side, and quite distinct 

 from the first. In Trichomonas, on the other hand, all four flagella 

 seem to emanate from one large four-cornered basal structure (fig. 7, 

 b and c). These varieties are obtained and examined in the manner 

 described on p. 38. 



